1. Field of the Invention
The present invention relates in general to an apparatus for reproducing images on a photosensitive recording medium by imagewise exposing the medium to a radiation influenced by an image on an original, and more particularly to such an apparatus capable of selectively practicing two different exposing methods wherein the original is differently positioned relative to the medium, namely, either spaced apart from the medium or superposed on the medium substantially in contact therewith.
2. Discussion of the Related Art
In the art of reproducing images on a photosensitive recording medium, the above two different exposing methods are known. In the first method, the original which bears an image to be reproduced is positioned in spaced-apart relation with the medium, and the original is irradiated with a radiation produced by a suitable light source. The medium is exposed to the radiation which is reflected by or transmitted through the original. The radiation is converged on the surface of the medium, through a suitable focusing lens, so that the image on the original is optically focused on the surface of the medium. Thus, the medium is imagewise exposed to the radiation. In this exposing method, the original is referred to as "focus-exposure" original, which is usually a slide film or transparency (e.g., 35-mm film). In the second method, the original and the medium are superposed on each other such that the two members are substantially in contact with each other. The medium is imagewise exposed to a radiation through the original. In this method, the original is referred to as "contact-exposure" original, which is usually semi-transparent.
Up to the present, there is known no image forming apparatus which is capable of selectively practicing the above-indicated two different exposing methods by using a single or common light source device for the focus-exposure original and the contact-exposure original.
Where a single light source is used in combination with a focusing lens for converging a radiation from the light source on the surface of the remotely located photosensitive medium, through the focus-exposure original, the focusing lens is required to exhibit a high degree of optical focusing characteristic. However, when the recording medium is exposed to the radiation from the common light source through the contact-exposure original in contact with the medium, the focusing lens is required to permit transmission of a relatively large amount of light toward the photosensitive medium. In this respect, it is noted that the contact-exposure Original may be a semi-transparent material such as an ordinary paper which bears a printed, drawn or written image, as well as a highly transparent slide film. Accordingly, the focusing lens should assure a relatively high level of illuminance on the surface of the contact-exposure original, rather than a high level of focusing accuracy as required in the exposing method using the focus-exposure original. Thus, the focusing lens used in combination with a single light source for both the focus-exposure original and the contact-exposure original is required to exhibit the two different optical characteristics, depending upon the exposing method. Where the lens permits transmission of a relatively large amount of light from the light source, the lens has comparatively small depth of focus and depth of field, and tends to cause poor focusing of the original image on the photosensitive medium. If the amount of light transmitted through the focusing lens is limited to assure high focusing accuracy, then a sufficient degree of illuminance cannot be obtained on the contact-exposure original, whereby the required exposing time is increased.
Where the common light source is used for the focus-exposure and contact-exposure originals, another problem may occur. That is, if the focus-exposure original is set in the apparatus while an image on the contact-exposure original is reproduced on the recording medium, the medium is exposed to the radiation which is influenced by the image on the focus-exposure original as well as the image on the contact-exposure original. In this case, the images on the two originals are superposed on the recording medium, unexpectedly to the user. In particular, the focus-exposure original, such as a 35-mm slide film or transparency, is usually small-sized and may frequently be overlooked when it is left in the apparatus. Further, it is relatively difficult to observe or perceive the content and posture of the image on the slide film, with naked eyes, and the wrong film may be set in the apparatus, or the film may be erroneously oriented or placed with the wrong side facing the light source.